Neplanocin A is represented by the following formula and one of carbanucleosides having strong antitumor activity, but it is not itself a sufficient drug for the clinical treatment of cancer, because of its strong adverse effect. ##STR1##
Nevertheless, there have been desired improved methods for efficiently preparing neplanocin A and related compounds.
Vandewalle et al. (Synlett, December 1991, 921-922) disclose the synthesis of (-)-neplanocin A starting from L-ribulose in 14 steps and in 15% overall yield. Ohira et al. (Tetrahedron Letters, vol. 36, No. 9, pp. 1537-1538, 1995) disclose the synthesis of (-)-neplanocin A starting from D-ribose modified with the protecting group in 9 steps and in 12% overall yield. Trost et al. (Tetrahedron Letters, vol. 38, No. 10, pp. 1707-1710, 1997) disclose the stereoselective synthesis of (-)-neplanocin A using an asymmetric catalyst in 13 steps and in 4% overall yield. Thus, the above prior processes require more improvement in the process step and yield.